Hydromechanical power transmission system

ABSTRACT

A hydromechanical power transmission system is disclosed, including a positive-displacement variable-speed piston-type hydrostatic power transmission driven by an input shaft and a coordinating planetary gear train connected to an output shaft. The hydrostatic transmission is made up of a variabledisplacement unit connected to the input shaft and usually acting as a pump and a constant-displacement unit positioned in series with the variable-displacement unit and usually acting as a hydraulic motor. A portion of the power input is transmitted to the output shaft through the hydrostatic transmission and the remaining portion is transmitted by the planetary gear train as a mechanical transmission unit so that the power transmission efficiency is higher than that attained in the conventional hydrostatic power transmission which is void of such mechanical transmission unit. A typical application of such transmission system is an automotive vehicle.

United States Patent [1 1 Mori HYDROMECI-IANICAL POWER TRANSMISSIONSYSTEM [75] Inventor: Yoichi Mori, Yokohama,.lapan [73 l Assignee:Nissan Motor Company, Limited,

Yokohama,Japan 22 Filed: Nov. 9, 1971 211 App]. No.: 197,105

[30] Foreign Application Priority Data Dec. 25, 1970 Japan 45/118133 v[52] [1.8. CI. 74/687 [51] Int. Cl. F l6h 47/04 [58] Field of Search60/53 B; 74/687, 74/690, 691

[56] References Cited UNITED STATES PATENTS 3,368,425 2/1968 Lewis74/687 X 3,283,612 11/1966 Densham 74/687 2,901,922 9/1959 Baker 74/6872,220,174 11/1940 Ravigneaux.... 74/763 X 2,646,755 7/1953 Jog 91/497 X2,772,755 12/1956 Nallinger et al. 91/498 X 3,489,036 1/1970 Cockrell eta1. 74/687 3,385,059 5/1968 Leonard et a1. 74/497 X PrimaryExaminer-Arthur T. McKeon Attorney-John Lezdey 57 ABSTRACT Ahydromechanical power transmission system is disclosed, including apositive-displacement variablespeed piston-type hydrostatic powertransmission driven by an input shaft and a coordinating planetary geartrain connected to an output shaft. The hydrostatic transmission is madeup of a variabledisplacement unit connected to the input shaft andusually acting as a pump and a constant-displacement unit positioned inseries with the variabledisplacement unit and usually acting as ahydraulic motor. A portion of the power input is transmitted to theoutput shaft through the hydrostatic transmission and the remainingportion is transmitted by the planetary gear train as a mechanicaltransmission unit so that the power transmission efficiency is higherthan that attained in the conventional hydrostatic power transmissionwhich is void of such mechanical transmission unit. A typicalapplication of such transmission system is an automotive vehicle.

9 Claims, '16 Drawing Figures PATENTEDUCTZB I973 3,766,804

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SHEET war 10 INVENTOR VO/Cl/l ml BY I ATTDRN HYDROMECHANICAL POWERTRANSMISSION SYSTEM This invention relates generally to powertransmission system and has its particular reference to ahydromechanical variable-speed power transmission system in which ahydrostatic power transmission is combined with a mechanicaltransmission unit. The hydromechanical power transmission system hereindisclosed is capable of steplessly delivering outputs of variedrevolution speeds from an input mechanical power having a fixed speedand, as such, is adapted to be used in an automotive vehicle driveline.

Hydrostatic power transmissions generally use a variable-displacementpump unit as a source of fluid power and a constant-displacement orvariabledisplacement hydraulic motor unit. Both the pump and motor unitsare usually of the piston type and are respectively connected tosuitable driving and driven members which may be input and output shaftsof a power train of an automotive vehicle. Power from the driving memberor input shaft is transmitted to the driven member or output shaft bythe aid of said fluid as a result of the pump delivery and the fluidpressure.

The positive-displacement piston-type hydrostatic power transmissionsare adapted to provide ease and simplicity of operation because of itsability to steplessly deliver outpus of various speeds from a source ofpower having a constant revolution speed and because of the fact thatthe stepless change of the revolution speed and even reversed motions ofthe motor unit can be effected without use of clutches and gearedreduction mechanisms. Less shocks and vibrations are invited than in thepurely mechanical power transmissions and the fluctuations in the torquetransmitted are largely subdued by the working fluid itself, thusdispensing with time and labour for the periodical inspection anmaintenance servicing of the transmission as a whole. Another advantageis that hydraulic braking actions are applicable during decelerationconditions.

In spite of these outstanding advantages over the me chanicaltransmissions, the hydrostatic power transmissions havedrawbacks in thatthe torque transmission efficiencies are apt to be degraded underlight-load and/or high-speed driving conditions and that the overallconstructions of the transmissions are intricate and disproportionatelylarge-sized for the transmission torque capacities required.

It is, therefore, an important object of this invention to provide a newand useful hydromechanical variablespeed power transmission system whichis simple in construction and economical to manufacture and in which thetorque is transmitted at a satisfactorily elevated efficiency throughoutvarious operational conditions.

The hydromechanical power transmission system to achieve this object isgenerally made up of a combination of a hydrostatic power transmissionand a cooperation planetary gear train as the mechanical transmissionunit. The hydrostatic power transmission includes avariable-displacement unit driven by an input shaft and aconstant-displacement unit whic coacts with the variable-displacementunit. The variable-displacement and constant-displacement units act as apump and a hydraulic motor, respectively, under various modes ofoperation of the hydrostatic transmission excepting the decelerationcondition. Each of the units includes a rotatable cylinder block and acam ring which is rockably positioned aroundthe cylinder block. Thecylinder block, in turn, comprises a plurality of generallyequidistantly spaced cylinders which are directed toward an axis ofrotation of the cylinder block and a plurality of ball piston elementswhich are respectively received in these cylinders in a manner to bemovable toward and away from the axis of rotation of the cylinder block.The cylinders may be constituted by cylindrical openings which areradially formed in the cylinder block. The cam ring of each cylinderblock has an internal circular cam surface to be engaged by theindividual ball piston elements.

The cam ring for the variable-displacement unit is position-adjustablewith respect to the associated cylinder block so as to vary the ratiobetween the displace-- ments of the variable-displacement and constantdisplacement units during operation. The cam ring is thus pivotallyconnected to a suitable stationary member such as a housing of thetransmission system and is rockable over the outer peripheral wall ofthecylinder block about the pivotal connection under the control ofactuating means. This actuating means is operable to displace the camring of the variable-displacement unit in a plane transverse to the axisof rotation of the associated cylinder block, thereby providingcontrolled degrees of eccentricity between the cam ring and the axis ofrotation of the cylinder block.

First and second pressure distribution passage means are provided in thehydrostatic transmission, leading from a source of a fluid underpressure and communicating with the variable-displacement andconstantdisplacement units to actuate these units by the fluid pressure.The first pressure distribution passage means is adapted to providefluid communication between those cylinders of the variable-displacementand constant-displacement units in which the ball piston elementsreceived therein are moved or being moved toward the axes of rotation ofthe cylinder blocks as they y revolve on the internal cam surfaces ofthecam rings. The second pressure distribution passage means, on theother hand, is adapted to provide fluid communication between thosecylinders of the variable-displacement units in which the ball pistonelements received therein are moved or being moved away from the axes ofrotation of the cylinder blocks. The delivery of the fluid from thevariable-displacement unit is thus varied over a stepless-range ineither direction from zero to maximum through reciprocating motions ofthe individual 1 ball piston elements of theunit. r i Theconstant-displacement unit of the hydrostatic power transmission isoperatively connected to the output shaft or the driven member throughthe planetary gear train above mentioned. This planetary gear train, theconstruction of which per se is well known in the art, comprises a firstrotary eleinent constantly driven by the input shaft, a second rotaryelement driven by the constant-displacement unit of the hydrostatictransmission and a third rotary element which is connected to the outputshaft.The input shaft extends through the hydrostatic transmissionbefore it terminates in the planetary gear train so that thetransmission system in its entirety can be of satisfactorily compact andsmallsized construction whichis ready to be assembled and installed in alimited working space. Because, moreover, the system according to thisinvention is arranged in a manner that a portion of the power from theinput I shaft is transmitted to the output shaft in a mechanicalfashion, namely, without resort to the fluid pressure, the totaltransmission efficiency can be increased to a considerable extent. Thehydromechanical power transmission system according to this invention isthus capable of transmitting a relatively large power for its simple andsmall-sized construction and is, therefore, specifically adapted for usein automotive vehicles.

The actuating means for the adjustable cam ring of thevariable-displacement unit of the hydrostatic transmission may bemanually operated but it is most preferable that such means beautomatically driven in response to desired or selected operationalconditions of, for example, the automotive vehicle whereby the deliveryof the fluid from the variable-displacement unit and accordingly thespeed reduction ratio can be regulated continually in accordance withthe varying operation requirements of the automotive vehicle. Theactuating means of this nature usually consumes a considerable amount ofpower in driving the adjustable cam ring so that the transmission systemrequires a supply of additional power for this particular purpose. Itis, therefore, another important object of this invention to provide anew and useful hydromechanical power transmission system having improvedactuating means capable of steplessly driving the adjustable cam ring ofthe constant-displacement unit of the hydrostatic transmission with aminimum of power requirement.

In the accompanying drawings:

FIG. 1 is a sectional view of a hydrostatic power transmission whichforms part of the hydromechanical power transmission system according tothis invention;

FIG. 2 is a cross sectional view illustrating a variabledisplacementunit of the hydrostatic power transmission shown in FIG. 1, this unitbeing illustrated as associated with cam ring actuating means which isshown in cross section;

FIG. 3 is a cross sectional view of a constantdisplacement unit of thehydrostatic transmission shown in FIG. 1;

FIG. 4A, 4B, 4C, 4D and 4E arediagrammatic view simulating the modes ofoperation of the hydrostatic power transmission shown in FIG. 1;

FIG. Sis a sectional view showing an overall construction of thehydromechanical power transmission system using the hydrostatictransmission shown in FIG. 1 and a planetary gear train which iscombined therewith;

FIG. 6 is a diagram indicating relations among the relative speeds ofrotation of the rotary elements of the planetary gear train shown aspart of thetransmission system illustrated in FIG. 1

FIG. 7 is a diagrammatic view indicating the basic mode of operation ofthe transmission system shown in FIG. 5;

FIG. 8 is a view similar to FIG. 5 but showing another form of thehydromechanical power transmission system according to this invention;

FIG. 9 is a diagram indicating relations among the relative speeds ofrotation of the rotary elements of the planetary gear train incorporatedin the transmission system shown in FIG. 8;

FIG. 10 is a diagrammatic view showing the basic mode of operation ofthe transmission system illustrated in FIG. 8;

FIG. 11 is also similar to FIG. 5 but now shows still another form ofthe hydromechanical power transmission according to this invention; and

FIG. 12 is a cross sectional view illustrating the constant-displacementunit of the hydrostatic transmission shown in FIG. 11.

Reference is now had concurrently to FIGS. 1 to 3 in which a preferredform of the positive-displacement piston-type hydrostatic transmissionwhich is to form essential part of the hydromechanical powertransmission system is illustrated. As seen in FIG. 1, the hydrostaticpower transmission intervenes between an input shaft 20 as a drivingmember and an output shaft 22 as a driven member. Where the showntransmission is to be incorporated in an automotive vehicle, the inputshaft 20 is driven by a crankshaft for a vehicle power plant such as aninternal combustion or gas turbine engine and the output shaft 22 isconnected to the vehicle traction wheels via a suitable driveline. Thehydrostatic transmission is encased in a power transmission housingwhich is generally indicated by reference numeral 24.

The hydrostatic power transmission as shown is made up of avariable-displacement unit 26 operable to deliver a fluid pressure and aconstant-displacement unit 28 which is operable to deliver a poweroutput in response to this fluid pressure. The variable-displacementunit 26 includes a cylinder block 30 which rotatable with the inputshaft 20 through a key 32 and supported on the transmission housing 24through a bearing 34. This cylinder block 30 has a generally circularcross section and is formed with a plurality of substantiallyequidistantly spaced piston cylinders which are shown to be constitutedby cylindrical openings or chambers 36a to 362 as seen in FIG. 2. It maybe noted that, although these cylindrical chambers are herein shown asfive in number, such is by way of example only and that the numberthereof can be selected as desired. Ball piston elements 38a to 38e arereceived in the cylindrical chambers 36a to 36e, respectively, in amanner to be slidable therein toward and away from the axis of rotationof the cylinder block 30. t

The cylinder block'30 is surrounded by an adjustable cam ring 40 havinga circular inner cam surface with which the individual ball pistonelements 38a to 38e are held in sliding engagement. This cam surface maybe annularly grooved as at 42, thereby adding to the area of contactbetween the ball piston elements and the cam ring. This cam ring 40 ispivotally supported by the transmission housing 24 through a pin 44 soas to be rockable over the outer peripheral wall of the cylinder block30, viz., in a plane transverse to the axis of rotation of the cylinderblock. The cam ring 40 thus being position-adjustable with respect tothe cylinder block, controlled degrees of eccentricity are providedbetween the cam ring and the axis of rotation of the cylinder blockdependingupon the angular position of the cam ring. This angularposition of the cam ring is continuously adjusted by suitable actuatingmeans which is to be described later.

The constant-displacement unit 28, on the otherhand, includes a cylinderblock 46 having a generally circular cross section and a rotatable camring 48 which is positioned around the cylinder block 46. The cylinderblock 46 is rotatable on the leading end portion of the input shaft 20through a bearing 50 and is supported by the transmission housing 24through a bearing 52, as illustrated in FIG. 1. The cylinder block 46has formed therein a plurality of cylindrical chambers, shown as five innumber by 54a to 54e in FIG. 3, which extend radially of the cylinderblock 46. These cylindrical chambers 54a to 542 receive therein ballpiston elements 560 to 56e, respectively, which are slidable toward andaway from the-axis of rotation of the cylinder block 46. The cylinderblock 46 of the constant-displacernent unit 28 is thus essentiallysimilar in construction to its counterpart is the variabledisplacementunit 26. Different from the unit 26, the cam ring 48 surrounding theindividual ball piston elements 56a to 56s of the constant-displacementunit 28 is integral with the cylinder block 30 of thevariabledisplacement unit so as to be rotatable on or with the cylinderblock 46 of the constant-displacement unit through a bearing 58. Inother words, the cam ring 48 of the constant-displacement unit isconstituted by a generally cylindrical extension of the cylinder block30 of the variable-displacement unit. The cam ring 48 has a circularinner cam surface which is engaged by the individual ball pistonelements 56a to 562 and, similarly to the cam ring 40 of thevariable-displacement unit, the cam surface of the cam ring 48 may beprovided with an annular groove 49 for the reason previously discussed.The cam ring 48 is positioned relative to the associated cylindricalblock 46 in a manner that a fixed degree of eccentricity is establishedbetween the cam ring 48 and the axis of rotation of the cylinder block46, as clearly seen in FIG. 3. This cylinder block 46 is integral withthe output shaft 22, as shown in FIG. ll.

First and second pressure distribution passage means are provided totransmit the torque from the variabledisplacementunit 26 to theconstant-displacement unit 28. These passage means are formed throughprovision of a valve sleeve 60 which is mounted between the input shaft20 and the cylinder block 30 of the variabledisplacement unit 26 andwhich is fast on the transmission housing 24. The first pressuredistribution passage means comprises an elongated groove 62 formedlongitudinally in the outer peripheral wall of the input shaft 20 and acircumferential port 64 which is formed in the outer peripheral wall ofthe valve sleeve 60 and which has a limited circumferential width asseen in FIG. 2. The elongated groove 62 merges at its end close to thecylinder block 30 of the variable-displacement unit 26 into an annulargroove 66 which is formed circumferentially in the outer peripheral wallof the input shaft 20. The circumferential port 64, on the other hand,

merges into a radial passage 68 formed in the valve sleeve 60. Theannular groove 66 and the radial passage 68 are at least partlycoextensive with each other so that communication is established betweenthe circumferential port 64 and the elongated groove 62 when the annulargroove 66 is aligned with the radial passage 68 as the input shaft 20rotates within the valve sleeve 60. The elongated groove 62,futthermore, merges at its end closed to the cylinder block 46 of theconstantdisplacement unit 28 into avcircumferential port 70 which isformed in the outer peripheral wallof the This circumferential portinput shaft 20 andwhich has a limited circumferential width as indicatedin FIG. 3. The second pressure distribution passage means, on the otherhand, comprises an elongated bore 72 which is formed in the input shaft20 and a circumferential port 74 which is formed in the outer peripheralwall of the valve sleeve and which has a limited circumferential widthas seen in FIG. 2.

74 is diametrically opposed to the circumferential port 64 of the firstpressure distribution passage means. This circumferential port 74 is atleast partly coextensive with an annular groove 76 which is formed inthe outer peripheral wall of the input shaft 20. This annular groove 76communicates with the circumferential port 74 through a radial passage78 formed in the valve sleeve 60 and with the bore 72 through a radialpassage 80, thereby providing communication between the circumferentialport 74 and the bore 72 in the input shaft. The input shaft 20 has inits outer peripheral wall adjacent the cylinder block 46 of theconstant-displacement unit 28 a circumferential port 82 which has alimited circumferential width and which is diametrically opposed to thecircumferential port of the first pressure distribution passage means.The circumferential port 82 communicates with the bore 72 in the inputshaft through a radial passage 84, thereby providing communicationbetween the circumferential ports 74 and 82 through the bore 72 in theinput shaft. The circumferential ports 64 and 74 of the first and secondpressure distribution passage means communicate with fluid passages 86and 88, respectively, which are formed in the transmission housing 24,as seen in FIG. 1. These fluid passages 86 and 88 are led from a sourceor sources of fluid under pressure and are respectively provided withone-way check valves to prevent leakage of the fluid when the fluidpressures reach the predetermined operating levels and with reliefvalves adapted to drain the fluid off when the fluid pressure rises toexcess levels, though not illustrated.

The cylindrical chambers 36a to 36e of the variabledisplacement unit 26merges at their innermost ends into respective radial ports 90a to 90ewhich are opened to the valve sleeve 60. These radial ports providefluid communication between some of the cylindrical chambers and thecircumferential port 64 of the first pressure distribution passage meansand between some of the cylindrical chambers and the circumferentialport 74 of the second pressure distribution passage means as thecylinderblock 30 rotates about its axis, as seen in FIG. 2. Likewise,the cylindrical chambers 54a to 542 of the constant-displacement unit 28merge into respective radial ports 92a'to 92e which are opened to theouter peripheral wall of the input shaft 20. These radial portsselectively provide fluid communication between some of the cylindricalchambers 54a to 54e and the circumferential port 70 of the firstpressure distribution passage means and between some of thesecylindricalchambers and the circumferential port 82 of the secondpressure distribution passage means, as the cylinder block 46.-rotatesabout its axis.

When, in operation, the input shaft 20 is driven for rotation, thecylinder block 30 is rotated through the key 32 interposed therebetween.This rotation of the cylinder block 30 is herein assumed to be aclockwise rotation in the cross sectional view of FIG. 2, as indicatedby an arrowhead therein. This causes the ball piston elements 38a to 382to move radially in therespective cylindrical chambers 36a to 362 withtheir outercause of the eccentricity between the cam surface and theaxis of rotation of the cylinder block 30 as illustrated. The ballpiston element 38b is moved to its innermost position, forced against aball seat (not numbered) defining the cylindrical chamber. As the ballpiston element 38a is thus moved away from the axis of rotation of thecylinder block 30, the fluid in the cylindrical chamber 36a is forcedinto the circumferential port 64 in the sleeve 60 through the radialport 90a. The fluid is fed to the circumferential port 70 for theconstant-displacement unit 28 via the radial passage 68, annular groove66 and elongated groove 61 and enters the cylindrical chamber 54a of theunit 28 through the radial port 92a. The ball piston element 56a isconsequently forced away from the axis of rotation of the cylinder block46 by the pressure of the fluid in the chamber 54a. The piston element56a is thus, forced against the inner cam surface of the cam ring 48 sothat the cylinder block 46 is rotated as the cam ring 48 rotates withthe cylinder block 30 of the variabledisplacement unit 26. Concurrentlyas the ball piston elements 38a and 56a of the variable-displacement andconstant-displacement units 26 and 28, respectively, are thus movedradially inwardly, the ball piston elements 38c and 560 are allowedoutwardly due to the increasing gaps between the cylinder blocks 30 and46 and the cam rings 40 and 48, respectively. The cylindrical chamber36c is thus supercharged with the fluid fed from the fluid passage 88via the circumferential port 74 and the cylindrical chamber 540supercharged with the fluid fed from this circumferential port 74through the annular groove 76 and the bore 72 in the input shaft 20.

Because, in this instance, the cam ring 48 of the constant-displacementunit 28 and the circumferential port 70 in the input shaft are revolvedat a common speed and because the degree of eccentricity between the camsurface of the ring 48 and the axis of rotation of the cylinder block 46is fixed, the rotational speed of the output shaft 22, viz., therotational speed of the cylinder block 46 of the constant-displacementunit 28 depends solely upon the amount of displacement of the fluid fromthe variable-displacement unit 26 to the constant-displacement unit 28through the first pressure distribution passage means. The displacementof the fluid from the variable-displacement unit, in turn, depends uponthe degree of eccentricity between the cam ring 40 and the cylinderblock 30 of the unit, viz., upon the angular position of the cam ring 40with respect to the cylinder block 30.

To aid in the clear understanding of the operation of the hydrostaticpower transmission above described, it is herein assumed that thetransmission has the following five modes of operation:

Mode A in which the displacement of the variable displacement unit isadjusted so that it equals the displacement of the constant-displacementunit.

Mode B in which the displacement of the variabledisplacem'ent unit isdecreased from the value in the Mode A to a lesser displacement.

Mode-C in which the cam ring 40 is positionedadjusted to be inconcentric alignment with the associated cylinder block 30 so that thedisplacement of the variable-displacement unit becomes zero.

Mode D in which the displacement of the variabledisplacement unit isfurther adjusted to decrease beyond the value in Mode C.

, Mode E in which the displacement of the variabledisplacement unit isadjusted in the opposite direction beyond the value in Mode A.

These different modes of operation of the hydrostatic power transmissionshown in FIGS. 1 to 3, viz., the changes in the rotational speed of thecylinder block 46 of the constant-displacement unit as a result of thechanges in the displacement of the variabledisplacement are nowdiagrammatically indicated in FIGS. 4A to 4E in which the rotary motionsof th cylinder blocks of the two units are translated into rectilinealmovements of reciprocating pistons in piston cylinders of a simulatedpower transmission. The simulated power transmission thus consists of avariabledisplacement unit 260 having a piston cylinder 360 and a piston380 and a constant-displacement unit 280 having a piston cylinder 540and a piston 560. Th piston cylinder 360 is divided by the piston 380into chambers 360a and 360b while the piston cylinder 540 is divided bythe piston 560 into chambers 540a and 540b. The chamber 360acommunicates with the chamber 540a through a passage 620 (indicated insolid lines) and the chamber 36Gb communicates with the chamber 54%through a passage 720 (indicated in broken lines) in figures exceptingFIG. D. In FIG. D, the chambers 360a and 540b are connected by a passage720 and the chambers 36011 and 540a interconnected by a passage 620, asindicated in broken lines. The piston 380 of the variable-displacementunit 260 is connected to a transmission housing 240 through a shaft 400and the piston cylinder 360 is connected to the piston 560 of theconstant-displacement unit 280 through a shaft 480 so as to be movablerelative to the cylinder 540. The cylinders 360 .and 540 are connectedto input and output shaft 200 and 220, respectively. The piston 560 ofthe constant-displacement unit 280 is thus moved back and forth by theinput shaft 200 through the cylinder 360 of the variable-displacementunit and the shaft 480. The variation in the diameter of the pistoncylinder 360 of the variable-displacement unit 360 represents thevariation in the displacement of the corresponding unit in the actualtransmission shown in FIGS. 1 and 2.

Thus, FIGS. 4A to 4E correspond to Modes A to E above defined.

Assuming that the input and output shafts 200 and 220 are driven atspeedsN and N respectively, and

- that rates of the variation in volume of the fluid in the variation involume of the vfluid in the variabledisplacement andconstant-displacement units 260 and I 280 are V and V respectively, perunit amount of displacement of each of the pistons 380 and 560 relativeto the associated cylinders 360 and 540, the fluid is delivered from thechamber 360a to the passage 620 at a rate of V,.N per unit time and thefluid thus delivered to the passage 620 is passed to the chamber 540a ata rate of V (N N per unit time under the modes of operation shown inFIGS. 4A, 4B and 4E. These rates must be equal to each other so that thefollowing equations hold:

hence,

If, thus, V, V as indicated in FIG. 4A, then N, so that no power outputis delivered to the output shaft and the transmission is held in aneutral condition. (Mode A) If 0 V V as indicated in FIG. 4B, then N, N'0 so that the output shaft is driven at a speed lower than the speed ofthe input shaft. (Mode B) If V, 0 as indicated in FIG. 4C, then thefluid flow path is interrupted so that N, N

The variable-displacement and constantdisplacement units thus act as apump and a motor, respectively, under those conditions which correspondto Modes A to C. If these units operate conversely as a motor and a pumpwith the inlet and outlet ports of the piston cylinder of thevariable-displacement unit conversed to each other as seen in FIG. 4D,then V 0 so that N N establishing an overdrive condition in thetransmission. (Mode D) If, lastly, V V as indicated in FIG. 4E, then N 0as is evident from the above equation so that the constant-direction ofthe motion of the variable displacement unit, establishing a reversedrive. (Mode E) With the above discussion in mind, reference is againmade to FIGS. 1 to 3.

When the transmission shown in FIGS. 1 to 3 oper-, ates under thepreviously defined Mode A which the cam ring 40 is adjusted in a mannerto make the displacement of the variable-displacement andconstantdisplacement units 26 and 28, respectively, equalized to eachother, no fluid pressure is carried to the cylindrical chamber 54a inthe cylinder block 46 of the constant-displacement unit 28 so that thecylinder block 46 and accordingly the output shaft 22 are held at astandstill. The transmission in its entirety is thus maintained 'in aneutral condition, as previously mentioned.

Under Mode B in whichthe displacement of the variable-displacement unit26 is decreased from the neutral value and consequently becomes smallerthan the displacement of the constant-displacement unit 28 a fluidpressure develops in the fluid chamber 540 of the constant-displacementunit so that the fluid under pressure .is now passed from this chamber54c to the chamber 54a which is approximately diametrical to the former,thus assisting in the rotational motion of the cylinder block 46 of theunit 28. The speed ratio between the input and output shafts is in thismanner decreased progressively, providing a so-called decelerationcondition. In this deceleration condition, the constant-displacementunti 28 acts as a pump while the variable-displacement unit 26 acts as ahydraulic motor.

When the cam ring 40 of the variable-displacement unit 26 is adjusted tobe concentrical with the associated cylinder block 30 so that thetransmission operates in Mode C, then the displacement of the variabledisplacement unit 26 becomes zero and accordingly a hydraulic lock isestablished in the constantdisplacement unit 28. The transmission nowacts as an integral unit so that the output shaft 22 is completelycoupled with the input shaft 20.

When the cam ring 40 of the variable-displacement unit 26 is furtheradjusted so as to have the displacement of the variable-displacementunit 26 reduced to minus values, the fluid in the cylindrical chamber36c which is roughly diametrically opposed to the chamber 36a of thevariable displacement unit is passed to the cylindrical chamber 54a ofthe constant-displacement unit 28 through the circumferential port 74 inthe sleeve 60, the bore 72 in the input shaft 20 and the cylindricalchamber 54c of the constant-displacement unit. The cylinder block 46 ofthe constantdisplacement unit overruns the cam ring 48 with the resultthat the output shaft 22 is driven at a higher speed than the rotationalspeed of the input shaft. An overdriving condition is thus achieved inMode D.

With the cam ring40 of the variable-displacement unit 26 conditioned sothat the displacement unit 26 is adjusted in the opposite directionbeyond the neutral condition, the ball piston elements 56a to 56e of theconstant-displacement unit 28 are caused to revolve in a directionopposite to the direction of rotation of the associated cam ring 48whereby the cylinder block 46 of the output shaft 22 is rotated in adirection opposite to the direction of rotation of the input shaft 20.Mode E thus establishes reverse drive.

It may be noted that the positional relationship between the cam ring 48of the constant-displacement unit 28 and the grooves, ports and passagesformed in the input shaft 20 is kept unchanged because the cam ring 48and the input shaft 48 rotate together.

The hydrostatic power transmission shown in F I68. 1 to 3 is thuscapable of varying the speed ratio between the input and output shaftssteplessly in either direction from zero to maximum under various modesof operation through adjustment of the adjustable cam ring of thevariable-displacement unit. Such adjustment of the adjustable cam ringmay be: effected in any desired manner insofar as the varyingoperational require ments imposed on the transmission are met continuously. FIG. 2 further illustrates a preferred example of the actuatingmeans which is adapted to automatically adjust the cam ring by means ofa minimum and mechanical operating effort.

Turning back to FIG. 2, the actuating means for the cam ring 40 of thevariable-displacement unit 26 includes a piston cylinder 94 havingopposite end walls 96 and 98 and a piston 100 which is slidable in thecylinder toward and from the end walls thereof. The piston cylinder 94is internally divided by the piston 100 into two chambers 102 and 104.Into these chambers 102 and 104 are opened fluid passages 106 and 108through ports 110 and 112, respectively. These fluid passage 106 and 108are branched from a main fluid passage 114 leading from a source (notshown) of fluid under pressure. Restrictions or orifices 116 and 118 aredisposed in the branch fluid passage 112 and 114, respectively, so thatthe fluid under pressure is passed to the chambers 102 and 104 atlimited rates. Bored piston rods 120 and 122 project from both faces ofthe piston 100, extending movably outwardly of the cylinder 94 throughthe opposite end walls 96 and 98 thereof. The piston rod 120 extendingthrough the end wall 96 has formed therein an axial bore 124 whilethepiston rod 122 has an axial bore 126 which terminates at a closedleading end (not numbered) of the piston rod 122. A rod valve 128extends into the bore 126 in the piston rod 122 through the bore 124 inthe piston rod 120 and a central aperture (not numbered) formed in thepiston 100. The two piston rods 120 and 122 being aligned together, thebore 124 in the piston 120, the central aperture in the piston 100 andthe bore 126 in the piston rod 122 are all in line with each other.Spaced annular grooves 130 and 132 are' formed in an inner peripheralwall of the piston 100 defining the central aperture therein. Theseannular grooves 130 and 132 communicate with the chambers 102 and 104through passages 134 and 136, respectively, which are formed in thepiston 100 as shown. The rod valve 128 has formed therein an axial bore138 which is opened into the bore 126 in the piston rod 122. This rodvalve 128 further has formed in its outer peripheral wall an elongatedgroove 140 communicating with the bore 138 through a passage 142 whichis also formed in the rod valve. The elongated groove 140 and thepassage 142 are located relative to the piston 100 in such a manner thatthey intervene between the annular grooves 130 and 132 when the rodvalve is in a neutral position. The bore 138 in the piston rod 122 isopened to the outside through a drain port 144.

' The piston rod 122 is in operative engagement with the cam ring 40 ofthe variable-displacement unit 26 through a connecting member 146, whichinterconnects the piston rod 122 and the cam ring 40 through pins 148and 148'. The rod valve 128, on the other hand, is connected to suitablecontrol means which is adapted to move the rod valve back and forthwithin the piston 100 and the piston rods 120 and 122 in response to theoperational conditions of the automotive vehicle on which thehydrostatic power transmission is installed.

When, now, the actuating means thus constructed is held in the neutralposition which is shown in FIG. 2, the piston 100 has its opposite facessubjected to a common fluid pressure which is passed to the chambers 102and 104 of the cylinder from the main fluid passage 114 through therestricted branch passages 110 and 112, respectively. The piston 100 andaccordingly the piston rods 120 and 122 are, therefore, held at astandstill with the elongated groove 140 in the rod valve 128 closed bythe central annular rim between the annular grooves 130 and 132 in thepiston. If, in this condition, the rod valve 128 is moved toward the endwall 98 of the cylinder 94, then the elongated groove 140 is permittedto communicate with the annular groove 132 in the piston 100 so that thefluid in the chamber 104 is drained through the passage 136, annulargroove 132, elongated groove 140, passage 142, bore 138 in the rod valve128, bore 126 in the piston rod 128 and drain port 144, in thissequence. The chamber 104'is replenished with the fluid through thebranch passage 112 but, since the rate of flow of the fluid through thisbranch passage is restricted by the orifice 118 and is consequentlylower than the rate of the flow through the drain port 144, the fluidpressure in in chamber 104 decreases progressively so that the piston isforced toward the end wall 98 under the influence of the fluid pressureobtaining in the chamber 102 until the elongated groove 140 is closed bythe central annular rim between the annular grooves 130 and 132 in thepiston. This causes the cam ring 40 to turn about the pin 44 through theconnecting member 146 with the result that the degree of eccentricitybetween the cam surface of the cam ring 40 and the axis of rotation ofthe cylinder block 30 is diminished with consequent reduction in thedisplacement of the fluid from the variabledisplacement unit 26. Themovement of the piston 100 is the opposite direction and the resultantmotion of the cam ring 30 are brought about in a manner similar to 12that above described and, therefore, no discussion thereabout will beherein incorporated.

It will now be appreciated from the foregoing description that thehydrostatic power transmission forming part of the hydromechanical powertransmission system according to this invention is capable of providingvarious modes of operation over a stepless range simply by regulatingthe angular position of the cam ring of the variable-displacement unit.Such transmission system is specifically adapted for use with anautomotive engine designed for air-pollution preventive purposes. Thetransmission system, however, will be well compatible with a gas turbineengine operating at an elevated speed during idling, because of itsability to achieve neutral, forward and reverse driving conditionssteplessly. The regulation of the angular position of the cam ring ofthe variable-displacement unit can be effected by a minimum of operatingeffort without resort to supply of supplementary mechanical power,because only a limited amount of reaction is imparted to the rod valveof the actuating means. The pressurized fluid act ing upon the piston todrive the cam ring is varied minutely in the cylinder chambers so thatthe cam ring can be moved softly and continually, thus preventing thevariable-displacement unit from being subjected to shocks and impactsduring operation.

These advantages of the hydrostatic transmission are amplified in thehydromechanical power transmission system implementing this invention inwhich the hdyrostatic transmission is combined with a planetary geartrain, a preferred embodiment of the transmission system being shown inFIG. 5.

In the embodiment shown, the power output of the hydrostatictransmission is delivered to the output shaft through the planetary geargrain which is generally denoted by reference numeral 150. The planetarygear train 150 comprises an internally toothed ring gear 152, at leastone planet pinion 154 meshing with the ring gear, and a sun gear 156meshing with the planet pinion. The ring gear 152 is integral with thecylinder block 46 of the constant-displacement unit 28 of thehydrostatic transmission, while the sun gear 156 is connected to theinput shaft 20. The planet pinion 154 is connected to the output shaft22 through a pinion carrier 158, as shown.

The relations among the relative speeds of revolution of the rotaryelements of the planetary gear train 150 are shown in the diagram ofFIG. 6, in which the three axes R, C and S of ordinate respectivelyindicate the revolution speeds of the ring gearl52, carrier 158 and sungear 156. The axes R and S are spaced apart from the axis C in a ratioof l l in which the value 1 represents a ratio' of the number of teethof the ring gear 152 to the number of teeth of the sun gear 156. Thepoints at which the axes R, C and S intersect an axis OO of abscissarepresent fixed or stationary conditions of the respective rotaryelements. The points on the axes R, C and S over this axis 0-0 ofabscissa thus indicate the speeds or revolution in a forward direction(i. e., the direction of rotation of the input shaft 20) of the rotaryelements, while the points on the axes R, C and S below the axis O-Orefer to the speeds of revolution in a reverse direction of the rotaryelements. With the convention thus made, the speeds of the rotaryelements in a given operating condition of the planetary gear train arerepresented by those points on the axes R, C and S which are situated ona single straight line. The revolution speed i of the sun gear 156depends upon the speed of rotation of the input shaft 20 while therevolution speed a of the ring gear 152 is dictated by the speed ofrotation of the cylinder block 46 of the constant-displacement unit 28.If, in this instance, the revolution speed a of the ring gear 152 isvaried from a, to a through a a and a with the revolution speed of thesun gear 156 fixed at i as illustrated, then the revolution speed b ofthe carrier 154 and accordingly the output shaft 22 varies from b to bthrough b b b and b respectively. Thus, a reverse drive condition isestablished when the ring gear 152 is rotated at a speedranging from a,to a The transmission system delivers no power output when the ring gear152 is rotated at speeda A deceleration condition is achieved when thering gear is driven at a speed ranging from a to a When the speed of thering gear reaches a then the transmission system in its entiretyoperates as an integral unit so that the power from the input shaft istransmitted to the output shaft 22 as it exactly is. An accelerationcondition is established when the ring gear is rotated at a speedintervening be tween a and a The operation of the hydromechanicaltransmission system shown in FIG. 5 is simulatively illustrated in FIG.7, in which the rotational motions in the actual transmission system aretranslated into rectilinear movements of functionally correspondingparts and elements. The planetary gear train 150 is herein simulated asa lever 150' having three spaced Working points 152', 156' and 158'which respectively correspond to the ring gear 152, sun gear 156 andpinion carrier 158. The points 152' and 156' are spaced from point 158'in a ratio of l I. As will be understood from this simulative diagram.The power to be transmitted to the output shaft 22 is the sum of thepower component transmitted from the sun gear 156 to the planet pinion154 and the power component transmitted from the ring gear 152 to theplanet pinion 154. The ratio of the torque transmitted by the sun gear156 to the torque transmitted by the ring gear 152 is l l and, since thesun gear and the planet pinion are drive at speeds i and a, the ratiobetween the powers transmitted thereby can be expressed as i.: la. Theoutput shaft 22 thus receives apower corresponding to i la. Although thepower 1' which is mechanically transmitted through the sun gear 156 ismaintained constant, the power la transmitted through the hydrostatictransmission varies with the value a. Since, moreover, a loss in thepower mechanically transmitted through the sun gear 156 is limited, theloss in thepower transmitted by the transmission system as a whole isconsiderably smaller than the loss which would be created where thehydrostatic transmission alone is used. The use of the planetary geartrain in combinationwith the hydrostatic transmission is alsoadvantageous because an increased transmission capacity is available inthe resultant hydromechanical transmission system by the additional,transmission capacity of the planetary gear train which in itself issimple in construction.

The planetary gear train forming part of the hydromechanical powertransmission system according to this invention may be utilized inmanners other than that shown in FIG. 5. FIG. 8 illustrates an exampleof such modified hydromechanical transmission system in which theplanetary gear train uses two different planet pinions. The planetarygear train, generally designated by reference numeral 160, now includesan internally toothed ring gear 162, first and second planet pinions 164and 166 carried by pinion carriers 168 and 170, respectively, and a sungear 172. The ring gear 162 is integral with the output shaft 22. Thefirst planet pinion 164 is in mesh with the sun gear 172 while thesecond planet pinion 166 is in mesh with both the first planet pinion164 and the ring gear 162. The sun gear 172 is connected to and drivenby the input shaft 20, as illustrated. Designated by reference numeral174 is a retainer plate which is secured; together with the pinioncarriers 168 and 170, to the cylinder block 46 of theconstant-displacement unit 28 of the hydrostatic transmission wherebythe planet pinions 164 and 166 are prevented from dislocated from theoperating positions.

The relations among the revolution speeds of the rotary elements of theplanetary gear train are shown in the diagram of FIG. 9, in which theaxes C, R and S of ordinate designate revolution speeds of the carriers168 and 170 and accordingly the cylinder block 46 of theconstant-displacement unit, ring gear 162 and sun gear 172,respectively. Different from the. diagram of FIG. 6, the axes R and Sare situated on the same side with respect to the axis C and are spacedapart therefrom in a ratio of l 1'. This is because of the fact that, ifthe sun gear 172 is rotated a full turn with the carriers 168 and 170held stationary, then the ring gear 162 rotates in the same directionand at an angle proportional to the ratio between the numbers of teethof the sun gear and the ring gear. If, as a result, the sun gear 172 isrotated with the input shaft 20 at speed i and the carriers 168 and 170are rotated with the cylinder block 46 of the constant-displacement unitat increasing speeds c c c c c and 0 then the output shaft 22 is rotatedwith the ring gear 162 at speeds d d d d d and d respectively.

FIG. 10 is a simulative diagram showing an operation of thehydromechanical power transmission system shown in FIG. 8. This diagramis essentially similar to the diagram of FIG. 7 except in that theplanetary gear train 160 is simulated as a lever 160 having spacedpoints 162' and 172' corresponding to the ring and aun gears 162 and172, respectively, which are situated on the same side to point 46corresponding to the cylinder block 46 or the carriers 168 and 170. Thepoint 162' corresponding to the ring gear 162 is connected to the outputshaft 220. Thus, the: ratio between the mechanically and hydraulicallytransmitted power components is expressed as i:(l l)c, in which thevalue 0 represents the revolution speed of the cylinder block46 of theconstant-displacement unit. The power transmission efficiency of thetransmission system shown in FIG. 10 is higher than that attained in thesystem shown in FIG. 5.

FIGS. 11 and 12 illustrate a third preferred embodiment of themechanical power transmission system according to this invention. Thetransmission system herein shown is constructed in a manner that therelationship between the cylinder block 46 and the ball piston elements56a to 56e of the constant-displacement unit 28 of the first embodimentis inverted whereby the cylinder block of the constant displacement unitis driven by the variable-displacement unit and the ring gear of theplanetary gear train is driven by the cam ring of theconstant-displacement unit. The planetary gear train used in thetransmission system shown in FIGS. 11 and 12 is exemplified, forconvenience sake,

Referring to FIGS. 11 and 12, the constantdisplacement unit, generallydesignated by reference numeral 176, includes a cam ring 178 which initself is similar to the cam ring 48 of the construction shown in FIG. 5but which is now integral with the ring gear 152 of the planetary geartrain 150. The cam ring 178 surrounds a cylinder block 180 which, inthis instance, is

integral with the cylinder block 30 of the variabledisplacement unit 26,as illustrated. The cylinder block 180 has formed therein a plurality ofsubstantially equidistantly spaced radial cylindrical chambers 182a andl82e which are herein shown as five in number by way of example. Thesecylindrical chambers 182a to 182e receive therein ball piston elements184a to 1848:, respectively, which are movable toward and away from anaxis of rotationoof the cylinder block 180. A valve sleeve 186 ispositioned between the input shaft and the cylinder block 180 in amanner to be rotatable with the cam ring 178 and accordingly with thering gear 152 of the planetary gear train. This valve sleeve 186 hasformed in its outer peripheral wall spaced circumferential ports 188 and190 which communicate, when the cylinder block 180 assumes that shownangular position, with the cylindrical chambers through radial ports192a and 192e formed in the cylinder block to open into the cylindricalchambers 182a and 182a, respectively. The circumferential port 188,furthermore, communicates with the circumferential port 70 through apassage 196 so as to establish fluid communication between the elongatedgroove 62 and the cylindrical chamber 182a. The circumferential port190, on the other hand, communicates with the radial passage 194 throughan annular groove 196 formed in an outer peripheral wall of the inputshaft 20, thereby providing fluid communication between the bore 72 inthe input shaft and the cylindrical chamber 1820. The hydromechanicalpower transmission system operates in a manner essentially similar tothe transmission systems previously described and, as such, thediscussion given therefore will apply to the system herein shown.

It will now be appreciated from the foregoing description tha thehydromechanical power transmission system according to this inventionhas, in addition to the features available in the hydrostatic powertransmission as formerly pointed out, outstanding advantages over theprior art hydrostatic power transmissions whichare void of themechanical power transmission unit such as the planetary gear train.Since, for instance, no clutches and geared reduction mechanisms areused in the transmission system according to this invention, thetransmission system in its entirety can be of simple and compactconstruction which is economical to manufacture. Because, moreover, aportion of the power to be transmitted is passed through an extension ofa single input shaft, a greater transmission capacity can be attainedthan in the prior art hydrostatic power transmissions. If, therefore, acertain transmission capacity is required of the transmission system,the system according to this invention can be of considerablysmall-sized construction. As compared with a transmission using paralleltransmission shafts, the transmission system according to this inventionhas its input and output shafts, hydrostatic transmission unit andplanetary gear train positioned in line with each other and, thus, canbe constructed more compactly.

What is claimed is:

1. A hydromechanical power transmission system comprising, incombination, a hydrostatic power transmission which includes avariable-displacement unit driven by an input shaft and aconstant-displacement unit; each of said units comprising a rotatablecylinder block and a cam ring having an inner'cam surface positionedaround said cylinder block, said cylinder block having a plurality ofsubstantially equidistantly spacedcylinders which are directed toward anaxis of rotation of said cylinder block and a plurality of ball pistonelements which are respectively received in said cylinders, said ballpiston elements being movable toward and away from the axis of saidcylinder block and in sliding engagement with the cam surfaces of thecam rings of the variable-displacement and constant-displacement units,said cylinder block of said variable-displacement unit being integralwith one of said cylinder block and said cam ring of saidconstant-displacement unit, said cam ring of said variable-displacementunit being pivotally supported to be rockable in a plane transverse tothe axis of rotation of said cylinder block of saidvariable-displacement unit, the position of an axis of said cam ring ofsaid constant-displacement unit being constant in respect to saidcylinder block thereof, actuating means which is operable to displacethe cam ring of said variable-displacement unit in a plane transverse tothe axis of rotation of the associated cylinder block for providingcontrolled degrees of eccentricity between the cam and said axis ofrotation of the cylinder block of the variable-displacement unit, firstpressure distribution passage means for providing fluid communicationbetween those cylinders of the variabledisplacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofsaid units as they revolve on the respective cam surfaces of the camrings of said units, and second pressure distribution passage means forproviding fluid communication between those cylinders of said Ivariabledisplacement and constant-displacement units in which the ballpiston elements received therein are moved away from said axes ofrotation of said cylinder blocks of said units, and a plantary geartrain including a first rotary element driven by said input shaft, asecond rotary element driven by said constant-displacement unit and athird rotary element connected to said output shaft.

2. A hydromechanical power transmission system comprising, incombination, a housing through which an input shaft and'an output shaftextend, a hydrostatic power transmission which includes avariabledisplacement unit having a cylinder block rotatable with saidinput shaft, said cylinder block being formed with a plurality ofsubstantially equidistantly spaced cylindrical chambers which aredirected toward an axis of rotation of said cylinder block, a pluralityof ball piston elements respectively received in said cylindricalchambers and movable therein toward and away from said axis, and anadjustable cam ring positioned around said cylinder block and pivotallyconnected to said housing for being rockable in a plane transverse tosaid axis, said adjustable cam ring having an inner cam surwith apluralityof substantially equidistantly spaced cy lindrical chambersdirected toward an axis of rotation of said cylinder block of saidconstant-displacement unit, a plurality of ball piston elementsrespectively received in said cylindrical chambers of saidconstantdisplacement unit and movable toward and away from the axis ofrotation of the cylinder block of said constant-displacement unit and arotary cam ring positioned around said cylinder block of theconstantdisplacement unit and having an inner cam surface with whichsaid ball piston elements of the constantdisplacement unit are insliding engagement, said rotary cam ring being integral with saidcylinder block of said variable-displacement unit, first pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variabledisplacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofthe variable-displacement and constant-displacement units as theyrevolve on the respective cam surfaces of the cam rings, second pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variable-displacement andconstant-displacement units in which the ball piston elements receivedtherein are moved away from said axes of rotation of said cylinderblocks, and actuating means which is operable to displace saidadjustable can ring in said plane for providing controlled degrees ofeccentricity between said adjustable cam ring and the axis of rotationof tha associated cylinder block, and a plane tary gear train comprisinga sum gear rotatable with said input shaft, at least one planet pinionmeshing with said sun gear and connected to said output shaft through apinion carrier, and an internally toothed ring gear-meshing with saidplanet pinion and rotatable with said constantdisplacement cylinderblock.

3. A hydromechanical power transmission system comprising, incombination, a housing through which an input shaft and an output shaftextend, a hydrostatic power. transmission which includes avariabledisplacement unit having a cylinder block rotatable with saidinput shaft, said cylinder block being formed with a plurality ofsubstantially equidistantly spaced cylindrical chambers which aredirected toward an axis of rotation of said cylinder block, a pluralityof ball piston elements respectively received in said cylindricalchambers and movable therein toward and away from said axis, and anadjustable cam ring positioned around said cylinder block and pivotallyconnected to said housing for being rockable in a plane transverse tosaid axis, said adjustable cam ring having an inner cam surface withwhich said ball piston elements are in sliding engagement, aconstant-displacement unit having a cylinder block rotatable on saidinput shaft and formed with a plurality of substantially equidistantlyspaced cylindrical chambers directed toward an axis of rotation of saidcylinder block of the constant-displacement unit, a plurality of ballpiston elements respectively received in said cylindrical chambers ofthe constantdisplacement unit and movable toward and away from the axisof rotation of the cylinder block of the constant-displacement unit anda rotary cam ring positioned around the cylinder block of theconstantdisplacement unit and having an inner cam surface with whichsaid ball piston elements of the constantdisplacement unit are insliding; engagement, said rotary cam ring being integral with saidcylinder block of said variable-displacement unit, first pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variabledisplacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofthe two units as they revolve on the respective cam surfaces of the camrings, second pressure distribution passage means for providing fluidcommunication be tween those cylindrical chambers of thevariabledisplacement and constant-displacement units in which the ballpiston element receive-d therein are moved away from the axes ofrotation of the cylinder blocks, and actuating means operable todisplace said adjustable cam ring in said plane for providing controlleddegrees of eccentricity between the adjustable cam ring and the axis ofrotation of the associated cylinder block, and a planetary gear traincomprisinga sun gear rotatable with said input shaft, first and secondplanet pinions in mesh with each other and rotatable with said cylinderblock of said constant-displacement unit through a carrier, and aninternally toothed ring gear meshing with said second planet pinion androtatable with said output shaft.

4. A hydromechanical power transmission system according to claim 1,further comprising a valve sleeve which is mounted between said inputshaft and said cylinder block of said variable-displacement unit andsecured to said housing, said first pressure distribution passage meansbeing formed by a first circumferential port formed in an outerperipheral wall of said valve sleeve and leading from a source of fluidunder pressure, said first circumferential port communicating with alimited number of the cylindrical chambers of said variable-displacementunit as the associated cylinder block rotates with said input shaft, anannular groove formed in an outer peripheral wall of said input shaftand communicating with said first circumferential port, an elongatedgroove formed longitudinally in the outer peripheral wall of said inputshaft, and a second circumferential port formed in the outer peripheralwall of said input shaft and communicating with a limited number ofcylindrical chambers of said constant: displacement unit as theassociated cylinder block rotates on said input shaft, said elongatedgroove merging into said annular groove and said second circumferentialport, said second pressure distribution passage means being formed by afirst circumferential port formed in an outer peripheral wall of saidvalve sleeve and leading from said source of fluid under pressure, saidfirst circumferential port of the second pressure distribution passagemeans communicating with another limited number of the cylindricalchambers of said variable-displacement unit as the associated cylinderblock rotates with said input. shaft, an annular groove formed in theouter peripheral wall of said input shaft and communicating with saidfirst circumferential port of the second pressure distribution passagemeans through a passage formed in said valve sleeve, an elongatedclose-ended bore formed in said input shaft and communicating with saidannular groove of the second pressure distribution passage means and asecond circumferential port formed in the outer pheripheral wall

1. A hydromechanical power transmission system comprising, incombination, a hydrostatic power transmission which includes avariable-displacement unit driven by an input shaft and aconstant-displacement unit, each of said units comprising a rotatablecylinder block and a cam ring having an inner cam surface positionedaround said cylinder block, said cylinder block having a plurality ofsubstantially equidistantly spaced cylinders which are directed towardan axis of rotation of said cylinder block and a plurality of ballpiston elements which are respectively received in said cylinders, saidball piston elements being movable toward and away from the axis of saidcylinder block and in sliding engagement with the cam surfaces of thecam rings of the variable-displacement and constantdisplacement units,said cylinder block of said variabledisplacement unit being integralwith one of said cylinder block and said cam ring of saidconstant-displacement unit, said cam ring of said variable-displacementunit being pivotally supported to be rockable in a plane transverse tothe axis of rotation of said cylinder block of saidvariable-displacement unit, the position of an axis of said cam ring ofsaid constantdisplacement unit being constant in respect to saidcylinder block thereof, actuating means which is operable to displacethe cam ring of said variable-displacement unit in a plane transverse tothe axis of rotation of the associated cylinder block for providingcontrolled degrees of eccentricity between the cam and said axis ofrotation of the cylinder block of the variabledisplacement unit, firstpressure distribution passage means for providing fluid communicationbetween those cylinders of the variable-displacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofsaid units as they revolve on the respective cam surfaces of the camrings of said units, and second pressure distribution passage means forproviding fluid communication between those cylinders of saidvariable-displacement and constant-displacement units in which the ballpiston elements received therein are moved away from said axes ofrotation of said cylinder blocks of said units, and a planetary geartrain including a first rotary element driven by said input shaft, asecond rotary element driven by said constant-displacement unit and athird rotary element connected to said output shaft.
 2. Ahydromechanical power transmission system comprising, in combination, ahousing through which an input shaft and an output shaft extend, ahydrostatic power transmission which includes a variable-displacementunit having a cylinder block rotatable with said input shaft, saidcylinder block being formed with a plurality of substantiallyequidistantly spaced cylindrical chambers which are directed toward anaxis of rotation of said cylinder block, a plurality of ball pistonelements respectively received in said cylindrical chambers and movabletherein toward and away from said axis, and an adjustable cam ringpositioned around said cylinder block and pivotally connected to saidhousing for being rockable in a plane transverse to said axis, saidadjustable cam ring having an inner cam surface with which said ballpiston elements are in sliding engagement, a constant-displacement unithaving a cylinder block rotatable on said input shaft and formed with aplurality of substantially equidistantly spaced cylindrical chambersdirected toward an axis of rotation of said cylinder block of saidconstant-displacement unit, a plurality of ball piston elementsrespectively received in said cylindrical chambers of saidconstant-displacement unit and movable toward and away from the axis ofrotation of the cylinder block of said constant-displacement unit and arotary cam ring positioned around said cylinder block of theconstant-displacement unit and having an inner cam surface with whichsaid ball piston elements of the constant-displacement unit are insliding engagement, said rotary cam ring being integral with saidcylinder block of said variable-displacement unit, first pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variable-displacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofthe variable-displacement and constant-displacement units as theyrevolve on the respective cam surfaces of the cam rings, second pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variable-displacement andconstant-displacement units in which the ball piston elements receivedtherein are moved away from said axes of rotation of said cylinderblocks, and actuating means which is operable to displace saidadjustable cam ring in sAid plane for providing controlled degrees ofeccentricity between said adjustable cam ring and the axis of rotationof tha associated cylinder block, and a planetary gear train comprisinga sun gear rotatable with said input shaft, at least one planet pinionmeshing with said sun gear and connected to said output shaft through apinion carrier, and an internally toothed ring gear meshing with saidplanet pinion and rotatable with said constant displacement cylinderblock.
 3. A hydromechanical power transmission system comprising, incombination, a housing through which an input shaft and an output shaftextend, a hydrostatic power transmission which includes avariable-displacement unit having a cylinder block rotatable with saidinput shaft, said cylinder block being formed with a plurality ofsubstantially equidistantly spaced cylindrical chambers which aredirected toward an axis of rotation of said cylinder block, a pluralityof ball piston elements respectively received in said cylindricalchambers and movable therein toward and away from said axis, and anadjustable cam ring positioned around said cylinder block and pivotallyconnected to said housing for being rockable in a plane transverse tosaid axis, said adjustable cam ring having an inner cam surface withwhich said ball piston elements are in sliding engagement, aconstant-displacement unit having a cylinder block rotatable on saidinput shaft and formed with a plurality of substantially equidistantlyspaced cylindrical chambers directed toward an axis of rotation of saidcylinder block of the constant-displacement unit, a plurality of ballpiston elements respectively received in said cylindrical chambers ofthe constant-displacement unit and movable toward and away from the axisof rotation of the cylinder block of the constant-displacement unit anda rotary cam ring positioned around the cylinder block of theconstant-displacement unit and having an inner cam surface with whichsaid ball piston elements of the constant-displacement unit are insliding engagement, said rotary cam ring being integral with saidcylinder block of said variable-displacement unit, first pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variable-displacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofthe two units as they revolve on the respective cam surfaces of the camrings, second pressure distribution passage means for providing fluidcommunication between those cylindrical chambers of thevariable-displacement and constant-displacement units in which the ballpiston element received therein are moved away from the axes of rotationof the cylinder blocks, and actuating means operable to displace saidadjustable cam ring in said plane for providing controlled degrees ofeccentricity between the adjustable cam ring and the axis of rotation ofthe associated cylinder block, and a planetary gear train comprising asun gear rotatable with said input shaft, first and second planetpinions in mesh with each other and rotatable with said cylinder blockof said constant-displacement unit through a carrier, and an internallytoothed ring gear meshing with said second planet pinion and rotatablewith said output shaft.
 4. A hydromechanical power transmission systemaccording to claim 1, further comprising a valve sleeve which is mountedbetween said input shaft and said cylinder block of saidvariable-displacement unit and secured to said housing, said firstpressure distribution passage means being formed by a firstcircumferential port formed in an outer peripheral wall of said valvesleeve and leading from a source of fluid under pressure, said firstcircumferential port communicating with a limited number of thecylindrical chambers of said variable-displacement unit as theassociated cylinder block rotates with said input shaft, an annulargroove formed iN an outer peripheral wall of said input shaft andcommunicating with said first circumferential port, an elongated grooveformed longitudinally in the outer peripheral wall of said input shaft,and a second circumferential port formed in the outer peripheral wall ofsaid input shaft and communicating with a limited number of cylindricalchambers of said constant-displacement unit as the associated cylinderblock rotates on said input shaft, said elongated groove merging intosaid annular groove and said second circumferential port, said secondpressure distribution passage means being formed by a firstcircumferential port formed in an outer peripheral wall of said valvesleeve and leading from said source of fluid under pressure, said firstcircumferential port of the second pressure distribution passage meanscommunicating with another limited number of the cylindrical chambers ofsaid variable-displacement unit as the associated cylinder block rotateswith said input shaft, an annular groove formed in the outer peripheralwall of said input shaft and communicating with said firstcircumferential port of the second pressure distribution passage meansthrough a passage formed in said valve sleeve, an elongated close-endedbore formed in said input shaft and communicating with said annulargroove of the second pressure distribution passage means and a secondcircumferential port formed in the outer pheripheral wall of said inputshaft and communicating with said bore and another limited number of thecylindrical chambers of the constant-displacement unit as the associatedcylinder block rotates on said input shaft.
 5. A hydromechanical powertransmission system comprising, in combination, a housing through whichan input shaft and an output shaft extend, a hydrostatic powertransmission which includes a variable-displacement unit having acylinder block which is rotatable with said input shaft, said cylinderblock being formed with a plurality of substantially equidistantlyspaced cylindrical chambers which are directed toward an axis ofrotation of said cylinder block, a plurality of ball piston elementsrespectively received in said cylindrical chambers and movable thereintoward and away from said axis, and an adjustable cam ring positionedaround said cylinder block and pivotally connected to said housing forbeing rockable in a plane transverse to said axis, said adjustable camring having an inner cam surface with which said ball piston elementsare in sliding engagement, a constant-displacement unit having acylinder block integral with said cylinder block of saidvariable-displacement unit on said input shaft and formed with aplurality of substantially equidistantly spaced cylindrical chambersdirected toward an axis of rotation of the cylinder block of theconstant-displacement unit, a plurality of ball piston elementsrespectively received in said cylindrical chambers of saidconstant-displacement unit and movable toward and away from said axis ofrotation of the associated cylinder block and a rotary cam ringpositioned around said cylinder block of the constant-displacement unitand having an inner cam surface with which the ball piston elements ofthe constant-displacement unit are in sliding engagement, first pressuredistribution passage means for providing fluid communication betweenthose cylindrical chambers of said variable-displacement andconstant-displacement units in which the ball piston elements receivedtherein are moved toward the axes of rotation of the cylinder blocks ofthe two units as they revolve on the respective cam surfaces of the camrings, second pressure distribution passage means for providing fluidcommunication between those cylindrical chambers of saidvariable-displacement and constant-displacement units in which the ballpiston elements received therein are moved away from said axes ofrotation of the two cylinder blocks, and actuating means operable todisplace said adjustable cam ring in said plane for providing contRolleddegrees of eccentricity between the adjustable cam ring and the axis ofrotation of the associated cylinder block, and a planetary gear traincomprising a first rotary element driven by said input shaft, a secondrotary element driven by said rotary cam ring, and a third rotaryelement connected to said output shaft.
 6. A hydromechanical powertransmission system according to claim 5, further comprising first andsecond valve sleeves respectively mounted between said input shaft andsaid cylinders of said variable-displacement and constant-displacementunits, said first valve sleeve being secured to said housing and saidsecond valve sleeve being rotatable with said rotary cam ring of theconstant-displacement unit, said first pressure distribution passagemeans being formed by a first circumferential port formed on an outerperipheral wall of said first valve sleeve and leading from a source offluid under pressure, said circumferential port communicating with alimited number of the cylindrical chambers of the variable-displacementunit as the associated cylinder block rotates with said input shaft, afirst annular groove formed in an outer peripheral wall of said inputshaft and communicating with said circumferential port, an elongatedgroove formed longitudinally in the outer peripheral wall of said inputshaft, a second annular groove formed in the outer peripheral wall ofsaid input shaft, said elongated groove merging into said first andsecond annular grooves, and a second circumferential port formed in anouter peripheral wall of said second valve sleeve for providing fluidcommunication beween said second annular groove and a limited number ofthe cylindrical chambers of said constant-displacement unit as theassociated cylinder block rotates on said input shaft, and said secondpressure distribution passage means being formed by a circumferentialport formed on the outer peripheral wall of said first valve sleeve andleading from said source of luid under pressure, said circumferentialport of the second pressure distribution passage means communicatingwith another limited number of the cylindrical chambers of saidvariable-displacement unit as the associated cylinder block rotates withsaid input shaft, a first annular groove formed in the outer peripheralwall of said input shaft and communicating with said circumferentialport of the second pressure distribution passage means, an elongatedclose-ended bore formed in said input shaft and communicating with saidfirst annular groove of the second pressure distribution passage means,and an annular groove formed in the outer wall of said input shaft andcommunicating with said bore for providing communication between saidsecond annular groove of the second pressure distribution passage meansand another limited number of the cylindrical chambers of saidconstant-displacement unit as the associated cylinder block rotates onsaid input shaft.
 7. A hydromechanical power transmission systemaccording to claim 1, in which said actuating means comprises a cylinderhaving opposite end walls, a piston slidable in said cylinder toward andaway from said end walls and having a central aperture formed therein,said cylinder being internally divided by said piston into first andsecond fluid chambers which communicate with a source of fluid underpressure through first and second fluid passages, said second chamberbeing opened to the outside through a drain port formed in saidcylinder, respectively, first and second piston rods projecting fromboth faces of said piston and axially movably extending outwardlythrough said end walls of the cylinder, said first piston rod havingformed therein an axial bore merging into said central aperture in saidpiston and said second piston rod having formed therein an axial boremerging from said central aperture and terminating close to a closedleading end of said second piston rod, a rod valve extending into thebore in said second piston rod through the bore in said first piston rodand said central aperture in said piston and axially movable in saidfirst and second piston rods and said piston, said rod valve havingformed therein an axial bore which is opened to said axial bore in saidsecond piston rod, first and second fluid passage means for selectivelyproviding fluid communication between said axial bore in said rod valveand said first and second fluid chambers, respectively, as said rodvalve is moved back and forth in said first and second piston rods, anda connecting member interconnecting said second piston rod and the camring of said variable-displacement unit for causing the cam ring to bedisplaced in said plane as said piston and said piston rods are movedrelative to said cylinder.
 8. A hydromechanical power transmissionsystem according to claim 7, in which said first and second fluidpassage means are formed by spaced first and second annular groovesformed in inner peripheral wall of said piston defining said centralaperture, first and second fluid passages formed in said piston toprovide constant fluid communication between said first and second fluidchambers and said first and second annular grooves in said pistonrespectively, and an elongated groove formed in an outer peripheral wallof said rod valve and located to intervene between said first and secondannular grooves in said piston, said elongated groove in said rod valvebeing in communication with one of said first and second annular groovesin said piston as said rod valve is axially moved in either direction.9. A hydromechanical power transmission system according to claim 1, inwhich each of the cam rings of said variable-displacement andconstant-displacement units has formed in its cam surface an annulargroove in which the ball piston elements in the associated cylinderblock slidably fit.